The present invention relates to passivation of the heavy metals in heavy metal-containing wastes. More precisely, it relates to methods of treating heavy metal-containing wastes suitable to passivating the heavy metals such as lead, cadmium, chromium and others in the wastes. The invention also relates to sealants suitable to the treatment. It further relates to solidified substances with high mechanical strength formed in the treatment.
Urban and industrial garbage and wastes are greatly increasing these days, and heavy metals often exist in the incinerated ash or fly ash discharged through incineration of such wastes. For protecting the environment, therefore, desired are some safe measures to make the incinerated ash or fly ash harmless.
One conventional method which has heretofore been proposed for that purpose comprises solidifying heavy metal-containing wastes with cement to thereby passivate the heavy metals in the solidified wastes. According to the method, however, it is difficult to completely passivate the heavy metals so as not to make them released at all from the solidified wastes. In addition, another problem with the method is that curing cement takes a lot of time.
Another method has been proposed, which comprises releasing the heavy metals from wastes by the use of mineral acids. However, the method is also problematic in that the metal-releasing acid treatment requires complicated operations and that an additional step of separately solidifying the wastes is needed.
On the other hand, disclosed is a method comprising adding a water-soluble sulfide, such as sodium sulfide, calcium sulfide or the like, to incinerator ashes and others discharged from usual incinerators, and kneading them to thereby passivate the heavy metals, such as lead, cadmium and others in the incinerator ashes and make them harmless, for example, in Japanese Patent Laid-Open Nos. 39262/1978, 1830/1980, 73091/1984, 111990/1988 and 24355/1997. In those, the method disclosed is to passivate the heavy metals in incinerator ashes into inert sulfides such as lead sulfide and others, thereby making them harmless. As a rule, however, the solubility of heavy metal sulfides in water is extremely low. Therefore, the particles of the heavy metal sulfides formed and deposited in the method are extremely fine, having a particle size of around 0.01 microns or so, and, in addition, many of them have relatively high dispersibility in water. For these reasons, the method disclosed is problematic in that the heavy metal sulfide particles formed therein pass through a paper filter having a mean pore size of 1 micron in the test stipulated in Notification No. 13 of the Director General of the Environment Agency of Japan. Japanese Patent Laid-Open No. 203981/1990 discloses a method of using a polymer substance with an organic carboxylic acid for solving the problem. However, the method is still problematic, as it is not economical.
Taking the above into consideration, we, the inventors have made the present invention, of which one object is to provide methods of treating heavy metal-containing wastes capable of efficiently and stably passivating the heavy metals in the wastes to thereby prevent the thus-passivated heavy metals from being released from the wastes.
Another object of the invention is to provide sealants and sealant promoters suitable to efficiently and stably passivating the heavy metals in heavy metal-containing wastes, etc.
Still another object of the invention is to provide compounds or compositions suitable to efficiently and stably passivating the heavy metals in heavy metal-containing wastes, etc. The compounds or compositions may be used as the sealant for passivating the heavy metals in heavy metal-containing wastes, etc.
Still another object of the invention is to provide solidified substances with high mechanical strength formed in the treating methods.
Specifically, the invention is summarized as follows:
(1) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes, (B) an alkali metal compound or an alkaline earth metal compound and (C) sulfur in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
(2) The method of above (1) for treating heavy metal-containing wastes, wherein the alkali metal compound or the alkaline earth metal compound (B) is an alkali metal or alkaline earth metal hydroxide or oxide.
(3) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes and (D) a sulfide in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
(4) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes, (B) an alkali metal compound or an alkaline earth metal compound, (C) sulfur and (E) a salt of a metal of which the standard electrode potential is higher than that of the cation of the component (B), in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
(5) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes, (B) an alkali metal compound or an alkaline earth metal compound and (C) sulfur in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture, and in which the component (A) and the component (C) are melted and kneaded before the component (B) is added thereto.
(6) A method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes, (D) a sulfide and (F) a salt of a metal of which the standard electrode potential is higher than that of the cation of the component (D), in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
(7) The method of any one of above (4) or (6) for treating heavy metal-containing wastes, wherein the sulfide (D) is an alkali metal or alkaline earth metal sulfide.
(8) The method of any one of above (1) to (7) for treating heavy metal-containing wastes, wherein the non-aqueous is at least one selected from sulfur, asphalt, thermoplastic resins and thermosetting resins.
(9) The method of above (1) for treating heavy metal-containing wastes, wherein the component (B) and the component (C) are individually in the form of master batch pellets with the non-aqueous medium (except sulfur).
(10) A solidified substance with high mechanical strength, which is formed in any one method of above (1) to (9).
(11) A sealant for heavy metals, which comprises (B) an alkali metal compound or an alkaline earth metal compound and (C) sulfur.
(12) A sealant for heavy metals, which comprises (B) an alkali metal compound or an alkaline earth metal compound, (C) sulfur, and a non-aqueous medium.
(13) The sealant for heavy metals of above (12), wherein the non-aqueous medium is at least one selected from sulfur, asphalt, thermoplastic resins and thermosetting resins.
(14) The sealant for heavy metals of any one of above (11) to (13), wherein the ratio of the alkali metal compound or the alkaline earth metal compound (B) to the sulfur (C), (B)/(C) by mol, falls between 0.2 and 3.
(15) The sealant for heavy metals of any one of above (11) to (14), wherein the alkali metal compound or the alkaline earth metal compound (B) is an alkali metal or alkaline earth metal hydroxide or oxide.
(16) An alkali metal or alkaline earth metal sulfide as obtained by reacting (B) an alkali metal compound or an alkaline earth metal compound with (C) sulfur with stirring at 50 to 170xc2x0 C. for 1 to 20 minutes.
(17) An alkali metal or alkaline earth metal sulfide of above (16), for which the ratio of the alkali metal compound or the alkaline earth metal compound (B) to the sulfur (C), (B)/(C) by mol, falls between 0.2 and 3.
(18) A sealant for heavy metals, which comprises the alkali metal or alkaline earth metal sulfide of above (16) or (17).
(19) The sealant of any one of above (11) to (15) or (18), which is for heavy metals in heavy metal-containing wastes.
(20) A sealant promoter for heavy metals, which comprises (B) an alkali metal compound or an alkaline earth metal compound, and a non-aqueous medium.
(21) The sealant promoter for heavy metals of above (20), wherein the alkali metal compound or the alkaline earth metal compound (B) is an alkali metal or alkaline earth metal hydroxide or oxide.
(22) A sealant promoter for heavy metals, which comprises (C) sulfur, and a non-aqueous medium.
(23) The sealant promoter for heavy metals of any one of above (20) to (22), wherein the non-aqueous medium is at least one selected from sulfur, asphalt, thermoplastic resins and thermosetting resins.
(24) The sealant promoter for heavy metals of any one of above (20) to (23), which is for heavy metals in wastes.
Modes of carrying out the invention are described below.
The first aspect of the invention is a method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes, (B) an alkali metal compound or an alkaline earth metal compound and (C) sulfur in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
The component (A) heavy metal-containing wastes to be treated in the invention includes garbage-incinerated ash, fly ash, polluted mud, slag, coal ash (a type of fly ash), sludge and other wastes containing heavy metals such as chromium, copper, cadmium, mercury, lead, etc. If containing water, it is desirable to dry the wastes before they are treated.
The component (B) alkali metal or alkaline earth metal compound is not specifically defined so far as it is a compound containing an alkali metal or alkaline earth metal. For example, it includes alkali metal or alkaline earth metal oxides, hydroxides, and even inorganic salts such as sulfates, chlorides, carbonates and others, organic salts such as carboxylates, oxalates and others, as well as alkoxides, chelate compounds and other various compounds of alkali metals or alkaline earth metals. Of those, preferred are alkali metal or alkaline earth metal oxides and hydroxides. The morphology of the compounds for use in the invention is not specifically defined, but preferred are solid compounds. The solid compounds may be in any form of powder, grains, etc. Substances containing alkali metal or alkaline earth metal compounds, such as cement, are also usable as the component (B) in the invention.
As specific examples of the component (B), mentioned are alkali metal compounds such as NaOH, Na2O, Na2CO3, KOH, K2O, etc.; and alkaline earth metal compounds such as Ca(OH)2, CaO, Mg(OH)2, MgO, etc. Of those, preferred are NaOH, CaO and KOH. One or more of these compounds may be used either singly or as combined.
Some heavy metal-containing wastes that contain a large amount of the component (B) in themselves, such as fly ash, do not require any additional component (B), and may be treated with the other components except the component (B) . For example, the amount of the component (B) to be in fly ash could be known on the whole by preparing an aqueous suspension of fly ash and measuring the pH of the suspension. Where the pH measured is not lower than 10, preferably not lower than 11, it is not always necessary to add some additional component (B) to fly ash. However, for ensuring complete passivation of heavy metals in the treated wastes, the component (B) will be added even to the wastes of that type.
The amount of the component (B) to be used varies, depending on the amount of the heavy metals in the heavy metal-containing wastes to be treated, but may be not smaller than the equimolar amount or so of the heavy metals in the wastes. For example, the heavy metal content of fly ash falls between 0.01 and 5% by weight. Therefore, the amount of the component (B) to be added to fly ash may be from 0.1 to 10 parts by weight or so, relative to 100 parts by weight of fly ash (in dry). If the amount of the component (B) added is too small, the heavy metals in wastes could not be sufficiently passivated. However, even if too large, such a large amount of the component (B) could no more augment its effect, and using too much component (B) will be uneconomical.
Sulfur for the component (C) is not specifically defined, and may be any ordinary simple sulfur. It may be obtained from natural resources, or may be produced in desulfurization of natural gas or petroleum fractions. The purity of sulfur for use herein is not required to be specifically high. Regarding its morphology, sulfur may be in any form of powder or liquid. As the case may be, excess sulfur will serve as the non-aqueous medium.
The amount of the component (C) sulfur may well be around 0.2 to 3 molar times that of the component (B), in order to sufficiently passivate heavy metals. For example, for fly ash, the amount of sulfur may fall between 0.1 and 10 parts by weight or so relative to 100 parts by weight of fly ash (in dry). If the amount of sulfur added is too small, the heavy metals in wastes could not be sufficiently passivated. However, even if too large, such a large amount of sulfur could no more augment its effect, and using too much sulfur will be uneconomical.
As the non-aqueous medium in which the components (A) to (C) are dispersed, preferred are sulfur, asphalt, thermoplastic resins, thermosetting resins, etc. The non-aqueous medium is necessary for solidifying wastes. Sulfur acts as a sulfidizing agent and also as a dispersion medium.
Sulfur for the non-aqueous medium may be any one mentioned hereinabove for the component (C). Sulfur for the component (C) may be the same as or may differ from that for the non-aqueous medium with respect to its composition and morphology. Where the two are the same, the amount of sulfur to be used shall be enough for its function to disperse the components (A) to (C) and for its function to passivate heavy metals.
Various types of asphalt may be used herein, concretely including native natural asphalt, and also petroleum asphalt such as straight asphalt, blown asphalt, asphaltic residue separated in deasphaltation, etc. The penetration of asphalt for use herein is not specifically defined. Herein preferred is asphalt having a degree of penetration of from 0.1 to 100. This is because asphalt of that type has the advantage of high flame retardancy and enhances the mechanical strength of the solidified substances of wastes and therefore the application of the solidified substances is greatly expanded. As the solvent for deasphaltation, preferred are propane, butane and their mixture.
The thermoplastic resins usable herein include, for example, polyethylenes, polypropylenes, polystyrenes, polycarbonates, nylons, polyvinyl chlorides, petroleum resins, etc.; and the thermosetting resins also usable herein include, for example, epoxy resins, xylene resins, diallyl phthalate resins, phenolic resins, unsaturated polyester resins, etc.
The amount of the non-aqueous medium to be used may fall generally between 10 and 1000 parts by weight, but preferably between 10 and 100 parts by weight, relative to 100 parts by weight of the heavy metal-containing wastes (in dry) to be treated.
In the invention, the components (A) to (C) are melted and kneaded in a predetermined ratio in the presence of a non-aqueous medium such as that mentioned above. Regarding the order of kneading them, it is desirable that the component (A) and the component (C) are first melted and kneaded and thereafter the component (B) is added thereto, melted and further kneaded.
The temperature at which the components are melted and kneaded is preferably not lower than 50xc2x0 C., but more preferably falls between 60 and 300xc2x0 C., even more preferably between 90 and 200xc2x0 C. The kneading time preferably falls between 1 and 40 minutes or so. In particular, after the component (C) is added to the component (A), the mixture may be kneaded for 1 to 30 minutes or so. After the component (B) is added thereto, the mixture may be kneaded for 0.1 to 20 minutes or so.
For melting and kneading the components, usable are any ordinary kneaders that are generally used for mixing and kneading powder and liquid. For example, usable are wheel-type, blade-type or roll-type kneaders.
After having been melted and kneaded, the resulting mixture is cooled and solidified whereby the heavy metals in the component (A) are passivated in the resulting solidified substance and are prevented from being released from it. In addition, the sulfudizing agent, if used excessively, is also prevented from being released from the solidified substance. After having been melted, the melt mixture could solidify within a few minutes even when it is left as it is. However, cooling the melt mixture in air or water is preferred, as the melt mixture can rapidly solidify.
As mentioned above, the components (A) to (C) are kneaded in melt in the presence of a non-aqueous medium, and then cooled and solidified whereby the heavy metals in the component (A) are passivated and are not released from the resulting solidified substance.
Preferably, the components (B) and (C) are separately melted and kneaded with the non-aqueous medium (except sulfur) to prepare master batch pellets, as the pellets are easy to handle.
The second aspect of the invention is described below.
The second aspect is a method for treating heavy metal-containing wastes, which comprises melting and kneading (A) heavy metal-containing wastes and (D) a sulfide in the presence of a non-aqueous medium, followed by cooling and solidifying the resulting melt mixture.
In this, the component (A) heavy metal-containing wastes to be treated is the same as that in the first aspect of the invention described above. Therefore, describing it is omitted herein.
Various types of sulfides are usable as the component (D), but preferred are sulfides of basic compounds, such as those with alkali metals or alkaline earth metals, or with ammonia, amines, anilines, etc. Concretely, they include sodium sulfide; sodium polysulfides such as sodium disulfide, sodium trisulfide, etc.; calcium sulfide; calcium polysulfides such as calcium disulfide, calcium trisulfide, etc.; potassium sulfide; potassium polysulfides such as potassium disulfide, potassium trisulfide, etc.; barium sulfide; barium polysulfides such as barium disulfide, barium trisulfide, etc.; as well as ammonium sulfide, sodium hydrosulfide, potassium hydrosulfide, etc. Of those, preferred are sodium polysulfides and calcium polysulfides. These sulfides may be used either singly or as combined.
The amount of the component (D) to be used varies, depending on the amount of the heavy metals in the heavy metal-containing wastes to be treated, but may be not smaller than the equimolar amount or so of the heavy metals in the wastes. For example, the heavy metal content of fly ash falls between 0.01 and 5% by weight. Therefore, the amount of the component (D) to be added to fly ash may be from 0.1 to 10 parts by weight or so, relative to 100 parts by weight of fly ash (in dry). If the amount of the component (D) added is too small, the heavy metals in wastes could not be sufficiently passivated. However, even if too large, such a large amount of the component (D) could no more augment its effect, and using too much component (D) will be uneconomical.
The non-aqueous medium in which the components (A) and (D) are dispersed is preferably selected from sulfur, asphalt, thermoplastic resins, thermosetting resins, etc., like in the first aspect of the invention. The non-aqueous medium additionally has the function of solidifying wastes. Specific examples of the non-aqueous medium and the conditions for kneading the components are the same as those in the first aspect of the invention, and describing them herein is omitted.
In the first and second aspects of the invention, metal salts such as those to be mentioned below may be additionally added to the system including the component (A).
Specifically, in the first aspect, (E) a salt of a metal of which the standard electrode potential is higher than that of the cation of the component (B), alkali metal or alkaline earthmetal, maybe added to the system; and in the second aspect, (F) a salt of a metal of which the standard electrode potential is higher than that of the cation of the component (D), that is, the metal constituting the sulfide of the component (D) may be added thereto. Specific examples of the metal for the component (E) in the first aspect or the component (F) in the second aspect include iron, aluminum, magnesium, zinc, copper, etc. The salts include, for example, sulfates, nitrates, carbonates, chlorides, hydroxides, etc. Specific examples of the salts are ferrous sulfate, ferric sulfate, aluminum sulfate, iron chloride, aluminum chloride, magnesium sulfate, iron hydroxide, aluminum hydroxide, etc.
The amount of the component (E) to be used may be generally from 0.5 to 5 times equivalents, but preferably from 0.7 to 3 times equivalent, more preferably from 1 to 2 times equivalents, relative to the number of equivalents as obtained by subtracting the number of equivalents of the heavy metals in the component (A) from the number of equivalents of the cation in the component (B). Similarly, the amount of the component (F) to be used may be generally from 0.5 to 5 times equivalents, but preferably from 0.7 to 3 times equivalent, more preferably from 1 to 2 times equivalents, relative to the number of equivalents as obtained by subtracting the number of equivalents of the heavy metals in the component (A) from the number of equivalents of the cation in the component (D).
The temperature at which the components are melted and kneaded in the process as above preferably falls between 90 and 200xc2x0 C., more preferably between 110 and 200xc2x0 C. If the temperature is lower than 90xc2x0 C., sulfur could not dissolve in the system and its sulfidization therein will be retarded. However, if higher than 200xc2x0 C., sulfur will form high-molecular substances thereby increasing the viscosity of the system. If so, kneading the system will require increased power. After the component (C) is added to the component (A), the mixture may be kneaded for 1 to 30 minutes or so. After the component (B) is added thereto, the mixture may be kneaded for 0.1 to 20 minutes or so.
In the embodiments where the component (E) or (F) is used, the non-aqueous medium to be used and also the conditions for melting, kneading, cooling and solidifying the system are the same as those in the others where neither the component (E) nor the component (F) is used. Therefore, describing them in detail herein is omitted.
In the first aspect of the invention where the component (E) is used and also in the second aspect thereof where the component (F) is used, the order of adding the component (E) or (F) to the system is not specifically defined. For example, in the first aspect, it is desirable that the component (E) is added to the system while or after the component (B) of (C) is kneaded in melt.
According to the treating method of the first and second aspects of the invention, not only the heavy metals in heavy metal-containing wastes can be passivated so as not to be released from the treated wastes but also dioxin can be sealed in the treated wastes.
The third aspect of the invention is described below, which provides compounds and also sealants or sealant promoters suitable to the method for treating heavy metal-containing wastes of the first and second aspects of the invention.
The first embodiment of the third aspect of the invention is a sealant comprising (B) an alkali metal compound or an alkaline earth metal compound and (C) sulfur.
The second embodiment thereof is a reaction product to be obtained by kneading (B) an alkali metal compound or an alkaline earth metal compound and (C) sulfur at a temperature falling between 50 and 170xc2x0 C. for 1 to 20 minutes, and a sealant comprising the reaction product.
The third embodiment thereof is a sealant comprising (B) an alkali metal compound or an alkaline earth metal compound, (C) sulfur, and a non-aqueous medium (except sulfur).
The fourth embodiment thereof is a sealant promoter comprising (B) an alkali metal compound or an alkaline earth metal compound and a non-aqueous medium (except sulfur), or a sealant promoter comprising (C) sulfur and a non-aqueous medium (except sulfur).
These embodiments of the third aspect of the invention are described in detail hereinunder.
In the embodiments of the third aspect, the component (B) and the component (C) may be the same as those in the first aspect of the invention described above. Therefore, the detailed description of concrete compounds of those components is omitted herein. As the alkali metal compound to be used herein, preferred are alkali metal oxides or hydroxides; and as the alkaline earth metal compound also to be used herein, preferred are alkaline earth metal oxides or hydroxides.
In the first embodiment, the component (B) alkali metal compound or alkaline earth metal compound is mixed with the component (C) sulfur, for which the amount of the component (B) may fall generally between 0.2 and 3 mols or so, but preferably between 0.3 and 2.5 mols, more preferably between 0.5 and 2 mols, relative to one mol of the component (C). If the amount of the component (B) is smaller than 0.2 mols for the component (C) of being one mol, the sulfidizing capability of the resulting product per the unit weight thereof will be poor. On the other hand, if a larger amount of the component (B) over 3 mols is mixed with the component (C), the excess component (B) could not react with it and will remain as it is. In addition, using too much component (B) is uneconomical.
Before mixed together, it is desirable that the components (B) and (C) are separately ground into small grains having a size of not larger than 5 mm, preferably not larger than 2 mm. If the grain size of the components is larger than 5 mm, the sulfidizing capability of the sealant to be obtained by mixing them will be poor.
In the first embodiment, it is desirable that the components (B) and (C) are, after having been mixed together, heated. This is the second embodiment.
In the second embodiment, the component (B), alkali metal compound or alkaline earth metal compound, and the component (C) sulfur are kneaded at a temperature falling between 50 and 170xc2x0 C., preferably between 60 and 150xc2x0 C., for 1 to 20 minutes to obtain a reaction product. If the temperature is lower than 50xc2x0 C., the alkali metal compound or the alkaline earth metal compound could not be sulfidized smoothly. On the other hand, however, if higher than 170xc2x0 C., sulfur polymerization will be accelerated. If so, kneading the components (B) and (C) will be difficult, and, in addition, the alkali metal compound or the alkaline earth metal compound could not be sulfidized to a, satisfactory degree. If the reaction time is shorter than 1 minute, the alkali metal compound or the alkaline earth metal compound could not be sulfidized smoothly. On the other hand, however, even if longer than 20 minutes, the reaction could not be promoted any more.
The components (B) and (C) to be kneaded may have various forms. Preferably, they are solid, powdery or flaky. The ratio of the component (B), alkali metal compound or alkaline earth metal compound, to the component (C) sulfur is the same as that in the first embodiment. Describing it is omitted herein.
In this embodiment, the components (B) and (C) having been kneaded and reacted in melt are cooled in an ordinary manner of, for example, spontaneous cooling, air cooling, water cooling or the like to give the intended reaction product. The reaction product thus obtained is extremely useful as a sealant for heavy metals such as those in heavy metal-containing wastes, etc. For a sealant, in general, the reaction product is cooled and solidified. As the case may be, however, the reaction product of the components (B) and (C) may be directly used as a sealant without being cooled. For example, heavy metal-containing wastes or others may be added to and kneaded in melt with the non-cooled reaction product, whereby the heavy metals in the wastes or others may be sealed with it.
The third and fourth embodiments are described below.
The component (B) is a strong alkali and is deliquescent, and therefore must be stored and handled with care. The component (C) belongs to the dangerous materials stipulated in the Fire Services Act, and its transportation and storage is strictly restricted. Therefore, it is desirable to use a mixture of the component (B) and/or the component (C) with a non-aqueous medium except sulfur, as a sealant as being safe and easy to handle. This indicates using the component (B) and the component (C) separately in the form of individual master batches.
Specifically, the third embodiment is a sealant comprising (B) an alkali metal compound or an alkaline earth metal compound, (C) sulfur, and a non-aqueous medium (except sulfur); and the fourth embodiment is a sealant promoter comprising (B) an alkali metal compound or an alkaline earth metal compound, and a non-aqueous medium (except sulfur), or comprising (C) sulfur, and a non-aqueous medium (except sulfur).
The third embodiment encompasses the mixture of the first embodiment and also the reaction mixture of the second embodiment, to both of which is added a non-aqueous medium except sulfur.
The non-aqueous medium for the third or fourth embodiment may be the same as that for the first aspect of the invention described above, but excluding sulfur.
In the third embodiment, the ratio of the component (B) alkali metal compound or alkaline earth metal compound to the component (C) sulfur may be the same as that in the first embodiment, and describing it herein is omitted.
The amount of the non-aqueous medium to be in the third embodiment varies, depending on its type, and therefore cannot be defined unconditionally. In general, it may fall between 5 and 1000 parts by weight, preferably between 10 and 500 parts by weight, more preferably between 50 and 200 parts by weight, relative to 100 parts by weight of the total of the components (B) and (C). If its amount is smaller than 5 parts by weight, the non-aqueous medium could hardly ensure safe and easily handlable master batches. On the other hand, however, even if a larger amount of the medium over 1000 parts by weight is mixed with the components (B) and (C), it could no more augment the intended effect.
In the fourth embodiment, the amount of the non-aqueous medium may fall generally between 0.1 and 50 parts by weight, preferably between 0.2 and 30 parts by weight, more preferably between 1 and 10 parts by weight, relative to one part by weight of the component (B) or (C). If its amount is smaller than 0.1 parts by weight, the non-aqueous medium could hardly ensure safe and easily handlable master batches. On the other hand, however, even if a larger amount of the medium over 50 parts by weight is mixed with the component (B) or (C), it could no more augment the intended effect.
More concretely, where the non-aqueous medium is asphalt for the component (B), the amount of the component (B) may generally fall between 1 and 1000 parts by weight, preferably between 10 and 500 parts by weight, relative to 100 parts by weight of asphalt. If the amount of the component (B) is too small, its master batch will be meaningless; but if too large, sufficiently covering the surface of wastes with asphalt will be impossible.
Similarly, where the non-aqueous medium is asphalt for the component (C), the amount of the component (C) may generally fall between 0.1 and 1000 parts by weight, preferably between 1 and 700 parts by weight, relative to 100 parts by weight of asphalt. If the amount of the component (C) is too small, the mixture could hardly exhibit its ability to passivate heavy metals; but if too large, the mixture will often ignite at room temperature and will continue to fire, and it shall be a dangerous material stipulated in the Fire Services Act.
In the third and fourth embodiments, the component (B) alkali metal compound or alkaline earth metal compound and/or the component (C) sulfur are/is kneaded with a non-aqueous medium at a temperature falling between 50 and 170xc2x0 C., preferably between 60 and 150xc2x0 C. for 1 to 20 minutes to prepare solidified substances. If the temperature is lower than 50xc2x0 C., the sulfidization of the alkali metal compound or the alkaline earth metal compound will be retarded; but if higher than 170xc2x0 C., sulfur will form polymeric substances and kneading the mixture will become difficult. In the latter, in addition, sulfur will react with the non-aqueous medium such as asphalt or the like to give hydrogen sulfide. On the other hand, if the reaction time is shorter than 1 minute, the sulfidization of the alkali metal compound or the alkaline earth metal compound will be retarded. However, even if the reaction time is prolonged over 20 minutes, the reaction could not be promoted any more. Like in the second embodiment mentioned above, the component (B) alkali metal compound or alkaline earth metal compound and the component (C) sulfur may be first kneaded, and then further kneaded with a non-aqueous medium to give the solidified substance of this embodiment. In this case, it is desirable that the kneaded blend of the component (B) alkali metal compound or alkaline earth metal compound and the component (C) sulfur is further kneaded with a non-aqueous medium at a temperature not higher than 170xc2x0 C., preferably not higher than 150xc2x0 C. If the kneading temperature is higher than 170xc2x0 C., the crystal water or the adsorbed water of the reaction product will be removed too rapidly. If so, the sulfidizing capability of the resulting solidified substance for passivating heavy metal ions will be poor.
In the invention, it is desirable that the solidified substances obtained in the embodiments noted above are ground into grains having a size of from 1 to 10 mm or so. The grains are referred to as master batch pellets, and are favorably used in the invention.
For example, the component (B) is stirred along with asphalt at 60 to 200xc2x0 C. for 0.1 to 10 minutes, then cooled, and thereafter ground into master batch pellets having a size of from 1 to 10 mm or so. Similarly, the component (C) is stirred along with asphalt at 60 to 150xc2x0 C. for 0.1 to 10 minutes, then cooled, and thereafter ground into master batch pellets having a size of from 1 to 10 mm or so.
Alternatively to the above, the master batch pellets of that type may also be produced by cooling the liquid drops of the melt mixture.
The amount of the components (A) to (C) and the non-aqueous medium to be the master batch pellets may be the same as that thereof not to be formed into master batch pellets.
As in the above, the sealant of the embodiments of the third aspect of the invention can be used for treating heavy metal-containing wastes so as to passivate the heavy metals in the treated wastes and to prevent them from being released from the treated wastes.
The solidified substances as formed in the treating methods of the first and second aspects of the invention have high mechanical strength and can be substituents for secondary products of concrete, such as constructional blocks of concrete, etc. In the first and second aspects of the invention, the melt mixture that contains heavy metal-containing wastes may be left as it is for a few minutes, and it may be solidified into high-strength solid substances. Preferably, however, the melt mixture is cooled with air or water, and it can be solidified more rapidly. The melt mixture can be molded with ease. Therefore, it may be filled into a predetermined form, and cooled therein. The resulting moldings can be substituents for secondary products of concrete, such as constructional blocks of concrete, etc. Before the melt mixture is solidified, if desired, it may be mixed with a filler (e.g., aggregate). The filler may be any of gravel, macadam and others, like that for ordinary cement or concrete construction.
The invention is described in more detail with reference to the following Examples, which, however, are not intended to restrict the scope of the invention.
Examples 1 to 22, Comparative Example 1, Reference Examples 1 to 11, and Control Examples 1 and 2 are to demonstrate the first and second aspects of the invention.
[Reference Example 1]
50 g of a chemical reagent, sulfur powder was put into a Teflon-coated metallic vat, the vat was put on a hot plate, and sulfur in the vat was heated up to 130xc2x0 C. 5 g of powdery sodium hydroxide was added to sulfur being kneaded with a spatula, and it changed brown. Next, 15 g of lead chloride was added thereto, and it immediately changed black. This was kneaded for further 30 minutes, and then cooled, and it solidified. The solidified product was subjected to a lead release test in the manner as follows: The solidified product was ground into grains having a size of at most 5 mm, and 50 g of the grains were sampled. 500 cc of water having a controlled pH value of 6.0 was added to the sample, and shaken continuously for 6 hours by the use of a shaker. Next, this was filtered through a glass paper filter having a pore size of 1 micron, and the lead concentration in the resulting filtrate was measured. It was not larger than 0.1 ppm, and was below the level defined for reclamation work.
In this Reference Example, lead chloride was used in place of wastes.